High softening point, low molecular weight epoxy resin

ABSTRACT

Epoxy resins which are diglycidyl ethers of tetrabromobisphenol A having a crystalline structure and in particulate form have an epoxy equivalent weight between 320 and 380 g/eq and a chlorine content that is smaller than 0.3%.

This application is a 371 of PCT/IL96/00094 fated Sep. 2, 1996.

FIELD OF THE INVENTION

This invention relates to epoxy resins and, more specifically, todiglycidyl ethers of tetrabromobisphenol A (hereinafter TBBA), having acrystalline structure and a higher softening point than like prior artresins having an amorphous structure.

BACKGROUND OF THE INVENTION

Diglycidyl ethers of TBBA are known in the art and have a wide varietvof applications, such as: raw materials for self-extinguishing epoxylaminates, flame retardants for phenolic laminates and for thermoplasticmaterials, raw materials for modified epoxy resins, and high molecularweight epoxy resins, powder coatings, dry epoxy molding compounds, heatstabilizers for halogenated organic compounds, and so forth.

The lower the molecular weight of the brominated epoxy resins, based ontetrabromobisphenol A, the lower their softening points are. Forexample, when the molecular weight decreases from 4,000 to 700 g/mol,the softening point decreases from 160° C. to 55° C. The handling andthe transportation of low softening point or semi-solid materials areboth complicated and expensive, since such materials tend to stick totheir containers. In some uses, such as in powder coating and solidmolding compounds, there is a need for high softening point materialswith high concentrations of epoxy groups, viz. with low molecularweight. It is possible, in principle, to raise the softening point bythe use of additives, such as materials having a high surface area, butthe presence of such material is not always acceptable, and anyway,their ability to raise to the softening point is limited.

It is a purpose of this invention to provide brominated epoxy resinsbased on TBBA, and specifically, diglycidyl ethers of TBBA, having a lowmolecular weight and a higher softening point than materials of the samemolecular weight known in the prior art.

It is another purpose of this invention to provide such resins having aspecific crystalline structure.

It is a further purpose of this invention to provide such resins with ahigh flowability in the particulate solid state (powder or flakes), thatare easy to package and to transport in bulk or bags.

It is a still further purpose of this invention to provide a method forproducing such resins, which is economical and has a substantiallyquantitative yield.

It is a still further purpose of this invention to provide a methodwhich has a very high and practically quantitative yield.

Other purposes and advantages of this invention will appear as thedescription proceeds.

SUMMARY OF THE INVENTION

The epoxy resins to which this invention refers are diglycidyl ethers oftetrabromobisphenol A, having the general formula ##STR1## wherein n hasan average value, in any batch of resins, between 0.0 and 0.2.

Said ethers have an epoxy equivalent weight (hereinafter EEW) between320 and 380 g/eq and a chlorine content that is smaller than 0.3%. Epoxyequivalent weight is given, per standard definition, by the molecularweight of the substance divided by the number of epoxy groups containedtherein. Such brominated epoxy resins can be produced from TBBAepichlorohydrine and sodium hydroxide as described, for instance, inPolymer Syntheses, Vol. II, S. R. Sandier and W. Karo, Academic PressInc., ISBN 0-12618502, pp. 80-81.

The product obtained from this synthesis according to the prior art isan amorphous product and is obtained in bulk form. The inventionprovides a product that is an epoxy resin having the aforesaid formulaand which is characterized by a specific crystalline form and has acorrespondingly increased softening point, which is generally about 100°and 120° C.

The specific crystalline form of the product is characterized by thepresence, in the diffraction pattern of the product, of the followingseven strong diffraction peaks:

d-value, Å

9.85

9.66

4.12

4.06

4.04

3.96

3.91

The invention further comprises a method for imparting to amorphousepoxy resin having the aforesaid formula, produced by prior art methodssuch as that hereinbefore mentioned, a crystalline structure and aconsequently higher softening point.

In a form of the invention, said method comprises crystallizing theproduct by heating to temperatures from 40° to 109° C., preferably from45° to 100° C. In a preferred form of the invention, the crystallizationof the product is carried out in the presence of seeding agents, whichare preferably crystals of the brominated epoxy resin being treated, andare used in an amount of less than 50% and preferably less than 10% byweight. The seeding crystals can be prepared by heating the amorphousproduct to 90° C. for 14 days. Their use accelerates the crystallizationprocess, which in their absence takes from 2 to 30 days, while in theirpresence is completed in 1 to 12 hours.

In another form of the invention, the amorphous brominated epoxy resinis dissolved in an organic solvent which is a weak solvent for thecrystalline resin. Examples of such solvents are toluene, benzene,xylene, methylethylketone, methylisobutylketone, acetone and mixturesthereof. Then, the resin is precipitated in crystalline form from thesolvent, either by cooling the solution or by adding co-solvents.Examples of such co-solvents are alcohols, such as methanol, ethanol,propanol etc. The precipitated crystals are then separated from thesolvent by filtration, washing, and evaporation. In this form of theinvention too, seeding crystals are preferably used in the precipitationstage.

Yu. M. Cheban et al., Dokl. Akad. Nauk USSR (1985), 283(3), 621-4describe the structure of monocrystals obtained by slow evaporation ofthe aforesaid diglycidyl ether of TBBA from alcohol-toluene solutions byslow evaporation. A similar study is reported by Yu. N. Safyanova et al.in Gor'k, Issled. Fiz.-Tekh. Inst., Gorkiy, USSR, Zh. Strukt. Khim.(1984), 25(4), 156-7. However, the slow evaporation is not an acceptableindustrial method, and further, it has a limited yield, as aconsiderable amount of the product remains in the solvent. In any case,the crystalline structure obtained by those authors is different fromthat according to the invention.

The crystalline epoxy resins according to the present invention may havevarious applications and are useful as flame retardants for phenolformaldehyde resin and for thermoplastic materials. Said crystallineepoxy resins are useful as raw materials for self extinguishing epoxylaminates and as raw materials for the preparation of modified epoxyresins or higher molecular weight epoxy resins. The crystalline epoxyresins according to the present invention are also useful as componentsof powder coating formulations or epoxy molding compounds.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following examples are illustrative of the invention, but have nolimitative significance.

EXAMPLE 1

500 g of a commercial diglycidyl ether of tetrabromobisphenol A, madefrom TBBA epichlorohydrine, as hereinbefore set forth, sold by Dead SeaBromine Group Ltd, hereinafter F-2200, and having the followinganalysis:

bromine content--48.5%

EEW--343 g/eq

hydrolyzable chlorine--0.02%

softening point--53° C. was heated to 90° C., whereby a thick, viscousmass was obtained. The mass was intimately mixed with one g ofcrystalline F-2200. The material was then spread onto a stainless steeltray to form a layer 3 mm thick. The tray was placed into an oven andheated to 90° C. for 12 hours. The resulting product is a whitecrystalline solid with a softening point of 111C and fusion heat of 38JIG.

Its diffraction pattern was determined as follows. X-ray data wereobtained with the Phillips Diffractometer PW 1050170, using Cu Kαradiation, Graphite monochromator, 40 kv, 28 ma. Said diffractionpattern exhibits the diffraction peaks listed hereinbefore.

EXAMPLE 2

200 g of F-2200 starting material of Example 1 were introduced with 100g of toluene into a 500 ml glass flask. The content of the flask washeated to 80° C. until complete solution was effected. The solution wasthen cooled to room temperature, and 2 g of crystalline F-2200 wereadded. The mixture was stirred for 12 hours at room temperature. A whitecrystalline solid was precipitated from the solution, which wasseparated from the liquid by filtration. The residual solvent wasevaporated from the solid by applying a vacuum of 3000 Pa and heating to80° C. 120 g of crystalline product, having a softening point of 111°C., were obtained. Its crystalline structure is essentially the same asthat of the product of Example 1.

The following Examples 3 and 4 illustrate uses of the products accordingto the invention.

EXAMPLE 3 Stabilization of HBCD

Hexabromocyclododecane (HBCD) is a flame or fire retardant (hereinaftersometimes abbreviated as FR) widely used in polystyrene foams. One ofthe limitations of HBCD is its low thermal stability. A good thermalstability is particularly important when plastic goods are manufacturedby extrusion of polystyrene foams or by injection molding of dense highimpact polystyrene and polypropylene. Common grades of HBCD start todecompose thermally at about 150° C., and, to avoid corrosion of theprocessing equipment, it is necessary to add large quantities (usuallymore than 5% by weight) of expensive thermal stabilizers. Such thermalstabilizers are lead dibasic phthalate, tin maleates, epoxies andpolyepoxide compounds. One of the problems with these stabilizers ishealth hazards which limit their use. For instance, thetris(2,3-epoxypropyl)isocyanurate (TEPIC), which is potentiallycarcinogenic, must be used with great precaution. Further, the use oflead stabilizers is often banned or strictly limited in manyindustrialized countries.

It is desirable to have grades of HBCD fire retardants having betterthermal stability than those of the prior art, thereby permitting theuse of higher processing temperatures and/or longer residence times athigh temperatures.

The purpose is achieved by using another brominated flame retardant asthermal stabilizer of the HBCD. Said brominated flame retardant ischosen in the family of the brominated epoxy resins, such as, forinstance, tetrabromobisphenol A diglycidyl ethers.

It was surprisingly found that the lower the molecular weight of thebrominated epoxy oligomer, the better the thermal stabilization of itsmixture with HBCD. A mixture of HBCD, manufactured and sold by BromineCompounds Ltd. under the denomination FR-1206, with differentstabilizers, have been prepared and their thermal stability has beentested by isothermal thermogravimetric analysis, evidencing aspectacular improvement for mixture of HBCD stabilized by a lowmolecular weight brominated epoxy resin according to the presentinvention. This is shown in table I:

                  TABLE I                                                         ______________________________________                                        ISOTHERMAL THERMOGRAVIMETRIC ANALYSIS                                           FOR HBCD STABILIZED WITH BROMINATED                                           EPOXY RESINS                                                                  (Under air)                                                                 ______________________________________                                        Stabilizer                                                                      EEW of stabilizer (g/eq) 343* 500                                                                               800                                           comparative comparative                                                   Composition                                                                     HBCD content (%) 85 85 85                                                     stabilizer content (%) 15 15 15                                             Thermal Stability at T =                                                        220° C.                                                                weight loss after  3 71 72                                                    20 min (%)                                                                  ______________________________________                                         *: from example 1                                                        

It was imposible to dry mix HBCD with low melting F-2200 as it sticks tothe mixer.

EXAMPLE 4 Preparation of Tribromophenol Modified Epoxy Resin

690 g of crystallized F-2200 made as in Example 1, 150 g of TBBA and450.0 g of 2,4,6-tribromophenol (hereinafter TBP), were loaded into a 1liter capacity separable flask equipped with thermometer and agitator.Then, the inner flask atmosphere was substituted with nitrogen gas, andthe mixture was heated and fused. Then, 1.3 g of 10% sodium hydroxideaqueous solution were added at 100° C., and a reaction was performed for12 hours at a temperature range between 150-180° C. With the reactionhaving been completed, the reaction product was drained into a stainlesspan, cooled and ground, and a lemon-yellow powder of the combustioninhibitor was obtained. EEW: 20000, softening point: 116° C., brominecontent 57%.

EXAMPLE 5 Comparative

Preparation of Tribromophenol modified epoxy resin In order to do thesame with low melt F-2200, it was melted at 120° C. and the melt wascharged to the reaction flask. Otherwise, the preparation wasessentially the same as in example 4.

While embodiments of the invention have been described by way ofillustration, it will be apparent that the invention may be carried outby persons skilled in the art, with many modifications, variations andadaptations, without departing from its spirit or exceeding the scope ofthe claims.

What is claimed is:
 1. Epoxy resins, which are diglycidyl ethers oftetrabromobisphenol A of the general formula ##STR2## wherein n has anaverage value, in any batch of resins, between 0.0 and 0.2, having anepoxy equivalent weight between 320 and 380 g/eq and a chlorine contentthat is smaller than 0.3%, which are crystalline and in particulateform, wherein their crystalline structure is characterized by thepresence, in the diffraction pattern, of the following seven strongdiffraction peaks:d-value, Å 9.85 9.66 4.12 4.06 4.04 3.96 3.91. 2.Resins according to claim 1, having a softening point from 100° to 120°C.
 3. Resins according to claim 1, in powder or flake form.
 4. Methodfor producing epoxy resins having a crystalline struture which arediglycidyl ethers of tetrabromobisphenol A, having the general formula##STR3## wherein n has an average value, in any batch of resins, between0.0 and 0.2, and having a high softening point, and wherein said epoxyresins have epoxy equivalent weights between 320 and 380 g/eq, whichcomprises producing such resins having an amorphous structure andimparting to them a crystalline structure.
 5. Method according to claim4, which comprises crystallizing the amorphous resin by heating it totemperatures from 40° to 109° C. and spreading the resin in thin layers.6. Method according to claim 5, which comprises crystallizing theamorphous resin by heating it to temperatures from 45° to 100° C. 7.Method according to claim 4, which comprises dissolving the amorphousresin is in an organic solvent which is a weak solvent for thecrystalline resin, and precipitating the resin in crystalline form fromthe solvent, by cooling the solution or by adding co-solvents.
 8. Methodaccording to claim 7, wherein the solvents are chosen from amongtoluene, benzene, xylene, methylethylketone, methylisobutylketone,acetone and mixtures thereof.
 9. Method according to claim 7, whereinthe co-solvents are alcohols.
 10. Method according to claim 9, whereinthe alcohols are chosen from among methanol, ethanol, propanol and thelike.
 11. Method according to claim 7, wherein the precipitated crystalsare separated from the solvent by filtration, washing, and evaporation.12. Method according to claim 5 or 7, which comprises carrying out thecrystallization in the presence of seeding agents, which are crystals ofthe resin being treated.
 13. Method according to claim 12, wherein theseeding agents are used in an amount of less than 50% by weight of theresin.
 14. Method according to claim 13, wherein the seeding agents areused in an amount of less than 10% by weight of the resin.
 15. A heatstabilizer for fire retardant compounds comprising crystalline epoxyresins which are diglycidyl ethers of tetrabromobisphenol A, having thegeneral formula ##STR4## wherein n has an average value, in any batch ofresins, between 0.0 and 0.2, and having a high softening point. 16.Flame retardants for phenol formaldehyde resin and for thermoplasticmaterials comprising crystalline epoxy resins which are diglycidylethers of tetrabromobisphenol A, having the general formula ##STR5##wherein n has an average value, in any batch of resins, between 0.0 and0.2, and having a high softening point.
 17. Raw material for selfextinguishing epoxy laminates or raw materials for the preparation ofmodified epoxy resins or higher molecular weight epoxy resins comprisingcrystalline epoxy resins which are diglycidyl ethers oftetrabromobisphenol A, having the general formula ##STR6## wherein n hasan average value, in any batch of resins, between 9.0 and 0.2, andhaving a high softening point.
 18. Components of powder coatingformulations or epoxy molding compounds comprising crystalline epoxyresins which are diglycidyl ethers of tetrabromobisphenol A, having thegeneral formula ##STR7## wherein n has an average value, in any batch ofresins, between 0.0 and 0.2, and having a high softening point.
 19. Aheat stabilizer for fire retardant compounds as in claim 15, whereinsaid epoxy resins have epoxy equivalent weights between 320 and 380 g/eqand chlorine contents that are smaller than 0.3%, which are crystallineand in particulate form, wherein their crystalline structure ischaracterized by the presence, in the diffraction pattern, of thefollowing seven strong diffraction peaks:d-value, Å 9.85 9.66 4.12 4.064.04 3.96 3.91.
 20. Flame retardants for phenol formaldehyde resin andfor thermoplastic materials as in claim 16, wherein said epoxy resinshave an epoxy equivalent weight between 320 and 380 g/eq and a chlorinecontent that is smaller than 0.3%, which are crystalline and inparticulate form, wherein their crystalline structure is characterizedby the presence, in the diffraction pattern, of the following sevenstrong diffraction peaks:d-value, Å 9.85 9.66 4.12 4.06 4.04 3.96 3.91.21. Raw material for self extinguishing epoxy laminates or raw materialsfor the preparation of modified epoxy resins or higher molecular weightepoxy resins as in claim 17, wherein said epoxy resins have an epoxyequivalent weight between 320 and 380 g/eq and a chlorine content thatis smaller than 0.3%, which are crystalline and in particulate form,wherein their crystalline structure is characterized by the presence, inthe diffraction pattern, of the following seven strong diffractionpeaks:d-value, Å 9.85 9.66 4.12 4.06 4.04 3.96 3.91.
 22. Components ofpowder coating formulations or epoxy molding compounds as in claim 18,wherein said epoxy resins have an epoxy equivalent weight between 320and 380 g/eq and a chlorine content that is smaller than 0.3%, which arecrystalline and in particulate form, wherein their crystalline structureis characterized by the presence, in the diffraction pattern, of thefollowing seven strong diffraction peaks:d-value, Å 9.85 9.66 4.12 4.064.04 3.96 3.91.
 23. A method for producing epoxy resins which arediglycidyl ethers of tetrabromobisphenol A as in claim 4 wherein saidepoxy resins are crystalline and in particulate form, wherein theircrystalline structure is characterized by the presence, in thediffraction pattern, of the following seven strong diffractionpeaks:d-value, Å 9.85 9.66 4.12 4.06 4.04 3.96 3.91.